Bitcoin is intimidating at first. Here is short explanation of bitcoin. First, remember it is volatile, but whatever amount you buy with fiat money (dollars, euros, yen, for examples), that amount is locked in, regardless of whether the bitcoin goes up or down. So, if you buy $100 of bitcoin using Coinbase, for example, they will take the money from your bank - which can take up to a week - and even though the bitcoin might increase or decrease in value - you will get $100 worth. You might ask, how long does a bitcoin transaction - by that I mean sending or receiving bitcoins, not purchasing or selling (back to the bank)? Normally, a sending or receiving transaction takes a few minutes, occasionally longer depending on how much traffic is happening in the entire bitcoin universe. It is a non-centralized system (which is why it's pretty secure), so there isno central hub like at a bank.

Coinbase lets you fund your purchase by bank transfer, and after a transaction or two, debit card (and I think credit card if you bank allows it). Once purchased, the bitcoins are stored in Coinbase in a personal "wallet". Then you send the bitcoin to someone else's wallet and he can withdraw from the wallet into his bank account. You can have many wallets, each with a unique identifier. In the same way, you can receive - someone send bitcoins to your wallet.

Now, there are kinds of wallets. Coinbase's is an online wallet, a "hot" wallet - not the most secure. There is also a "cold" wallet, which is stored offline, like on a USB stick. Much safer. And there are third party wallets, like the Mycellium app - which is a hardware wallet, almost "cold", in that the wallet exists on your phone.

If you want sell bitcoins, you have to use a bitcoin platform that supports withdrawals to a bank account. Not all do. Some are just platforms for trading and sending, like Mycellium. In order to sell from that sort of platform, you have to send your bitcoins to another platform like Coinbase, then withdraw to the bank.

You may ask why use something like Mycellium if you can't withdraw the money. Well, since bitcoin transactions are hard to trace (but far from impossible!!!!! - remember that), you could accept the bitcoins from someone on one platform, then move it through one or two others before cashing out (withdrawing). However, as I wrote above, bitcoins are volatile, so after a few transactions to move them around, you may end up with less fiat money than you anticipated.

Some bitcoin platforms are limited to buying with one currency, some are multicurrency. Bitcoins themselves do not depend on the currency you buy them with or withdraw to a bank. Bitstamp, for example, lets you buy or sell in dollars or euros. Best to do some research on a good platform that lets you also do withdrawals. Bitstamp, Coinbase, Kraken are ones I've checked out that do. Others, like Coinmama don't allow withdrawals.
Also, in choosing a platform, find one that is easy to use. Coinbase, for example is pretty easy. However, their fees aren't the lowest.

And that's another point - fees. Each platform has it's own fee schedule, so review the fee structure of the different platforms. The fees generally apply to purchasing and withdrawing bitcoins. Wallet-to-wallet transaction fees, on the other hand, are usually a small fraction of the transaction - you will barely notice those.